There is a known imaging device for detecting a main subject, particularly the face of a person, through image recognition, to adjust a focal length and the like by use of a result of the detection. Also, for example of such an imaging device, Japanese Patent Laid-open Publication No. 2003-107335 discloses a first known conventional imaging device which performs a face detection and sets a region detected as a focus adjustment region. Further, Japanese Patent Laid-Open Publication No. 2006-60329 discloses a second known conventional imaging device which decides a main subject by detecting a skin color thereof and follows the main subject using pattern matching, for example. Such imaging devices are suitable for taking portrait pictures so that they are useful especially for novice users not familiar with manipulation to a camera.
Moreover, Japanese Patent Laid-Open Publication No. 2003-92699 discloses a third known conventional imaging device which detects not only a single main subject but also a plurality of subjects in a captured image to make a control to have all of the subjects in focus. Such an imaging device is good for shooting a plurality of people as a subject such as in commemorative photographs.
In addition, in terms of detection processing, the operation to follow the main subject determined using pattern matching as the one described in Japanese Patent Laid-Open Publication No. 2006-60329 is made by following the main subject by use of a previous detection result, thereby making it possible to perform the detection at a higher speed than to detect a subject anew in an entire image, and to quickly follow the subject according to movement of a person or a change of angle of view.
A difference in the processing speed will be described with reference to FIGS. 3A and 3B
In FIG. 3A, the number 100 represents image data obtained by continuously capturing an image and to be displayed on a display part such as LCD in order to decide a framing of the image during a standby period for shooting. The number 101 represents image data used in the face detection processing, and the arrows between the image data 101 represent a period in which the detection processing is being performed. This face detection processing is performed by intermittently selecting data from the image data captured for the purpose of shortening a time-taking detection processing time.
In contrast, FIG. 3B shows a face following processing to be performed once the face is detected.
The number 102 represents image data used in the face following processing, and the arrows between the image data 101 represent a period in which the face following processing is being performed. As shown in FIG. 3B, in the face following processing, the face detection is made at a higher speed than when a face is detected anew, enabling a detection result to be obtained at a shorter interval.